



circuits and trunk conductors. Fig. 6, is a detail in elevation of the visual indicator.

Considering first, Figs. 1 and lf, A is the terminal switchboard subdivided into sections a, a2, 0.3, dac.; and B is the connecting switchboard. Any number of substation lines may converge to the central station, but for perspicuity l have in Figs. l and 2 of the several drawings shown but two; and that number is sufticient for explanatory purposes, since no further principle of operation is involved in the addition of others. L and L2 represent these two circuits which extend respectively from substations S and S2; L passing the spring jacky' at the connecting board, and its jack J at section a of the terminal board successively, and normally connecting them with its regular call annunciator drop Z; While L2 in the same way, passes .its jacksj2, J2 and reaches its call drop Z2. From each terminal section a, one or more trunk conductors as O in Fig. l, and O, O2, O3, O4 in Fig. la, are extended to suitable points in front of, and adjacent to, the connecting switchboards B, and are at both of their ends provided (as will be hereinafter more particularly specified) with suitable connection devices whereby at the terminal board end, they may be united with any main circuit so as to form an extension of such main circuit to a point at the connecting board near to the jack of the line wanted there, and whereby at the said connecting board they may form a conveniently manipulated union with such line. At each terminal section a is also the usual number of link connectors consisting each of flexible conductors having at each end a connecting plugadapted to bethrust intospringjacks, and by these, connections may be made between any two line jacks J, if the call be for a circuit terminating on the same or the immediately adjacent section on either side; or between any line jack J, and a trunk jack 76,'for connections which are to be made through the connecting board. These links c are shown in Figs. 1 and l, and a disconnecting drop D is shown as being included in circuit therewith.

I place at the connecting board springjack of each main circuit a visual signal indicator V, which becomes operative whenever a plug is inserted in the terminal board jack of such circuit, and at each of the latter jacks is a similar Visual signal indicator V2 respon` sive to the placing of a connecting plug in the corresponding connecting board jack of the same line. The trunk conductors also are at their terminal boards provided each with a similar indicator t to denote aconnection or disconnection effected at their other end; and are likewise provided at their terminalboard ends with an annunciator drop Z from which they are disconnected when in use, but which on the withdrawal of the terminal board plug resumes its connection so that upon it, should a main circuit not be promptly disconnectedfrom its trunk at the connecting board, the calls of said line may be received.

From suitable springjacks 13 at the termiminal board sections, order or instruction telephone circuits 12 extend t0 operators telephones 5 Worn or used by the operators at the connecting board. Y One such circuit to each connecting board operator will ordinarily be sufficient, and the several stem circuits 12 may have branches 14: to the spring jacks 13 at each section, the said circuits being normally open in each springjack until the section operators telephone circuit plug is inserted in said jack. The terminal and connecting boards may be in the same room, or otherwise, as preferred.

The foregoing description generally outlines the essentials of my invention and referring to Figs. 2 to 6, I will Vnow proceed to specify its details of construction and operation. Two main circuits only are indicated in the diagram, as all are arranged and worked in the same way, and vto delineate a greater number would, would simply complicate withoutfurther elucidating the drawing. The dil agram, Fig. 2, then represents two main circuits L and L2 extending respectively from telephone stations S and S2 to the central station where each passes through a springjack j jg on the connecting board B, to a second springjack J or J 2 on the terminal board: circuit L however terminating at section d, and circuit L2 at section a4. The connecting and terminal switchboard portions of the apparatus are shown as being separated by the median line a: Since metallic circuits are rapidly coming into general use, I have shown L2 as a metallic circuit. Lis an earth completed circuit, but after reaching the terminal board, it is extended backwardly and is grounded at g, after its extension also passes through the jack j at the connecting board. All of the springjacks used in this system maybe made alike, although they may be connected differently.

Any well known form of four contact springjack may be employed, and the plug intendp ed for use therewith, must also of course have four contacts, or be adapted to control four contacts.` Fig. 5 illustrates in plan and side view a form which I have found convenient., and which also is the form indicated in Fig. 2. It comprises Ytwo horizontally disposed contactV springs 3 and It pressing normally against resting or anvil contacts 8 and 7; and two other contact springs 5 and 6 also placed horizontally but edgewise, so that their iiat surfaces oppose the edges of the former. These have no normal contacts, but so long as the jack is at rest, may form discontinuous portions of a circuit. The several plug connectors shown,-P, P2, and P3, may all also be of like construction, and have four in- :sulated conducting surfaces mounted on a suitable non-conducting stem i, and each adapted to. register and make contact with some one of the jack springs. Thus when IOC link connection, if any of the appliances of the operator are to be used thereon, they are connected in bridge circuit between the two main conductors y and y2. To this end, the two principal conductors 37 and 38 of the cam switch lead from points e and e2 on the link conductors y and y2 respectively, and at the points es and c4 branch to two sets of contacts. One of the pairs of branches ends in terminals n and n2 which may connect with the telephone loop; and the other ends in terminals d and d2 which connect alternatively with the disconnecting drop or generator loop. In the normal position of the cam lever which is upright, the telephone and generator loops are both open, but the disconnecting drop D is in circuit between the conductors y and y2 through the contacts d, c2, and d2, c3. In the second position of the cam when depressed to one side in which a call is to be sent to line, the telephone and disconnecting drop loops are both open, and the generator is connected between the conductors y and y2 through the contacts d h4 and d2 h3, the original contacts of d and d2 with c2 and c3 having been forced apart by the descending spindle and wedge, which projects downwardly under the influence of the cam, as shown in Fig. 3. But if the cam be turned reversely into its third position, the telephone loop being controlled by a second spindle will be closed in bridge circuit with the main conductors y and y2 through the contacts n, h, n2, h2, without opening the circuit of the disconnecting drop, the impedance of this, being sufcient to prevent any short circuiting of the telephonie currents.

Although it is true that while the connection link Y is employed at both ends inuniting two main circuits, the telephone loop (should it be connected) is indeed bridged between its two conductors, or in other words is in derived circuit with the two said circuits, it is also true that when one of the plugs P only of such link is in use, as in answering a call, the other plug remaining unused, the telephones although connected in the same way, are yet in direct circuit with the said plug, the alternative route through the second plug being for the present discontinuous. When answering calls therefore, the answering end of the connection link Y is in fact itself the telephone loop, and the answering plug, the plug terminal of such loop.

The instruction or order circuits l2, extend between each section of the terminal board and the several operators telephones at the connecting board. Their general arrangement has already been described. This also is here shown as being a metallic circuit, the two conductors thereof, r and r2 both extending from the head telephone t3 of the connecting board to a spring jack 13 at a section a of the terminal board. To indicate that said order circuit passes likewise to other sections, the rudimentary branches 14 are shown, connecting with the conductors of circuit l2. Being common to a plurality of section's, it is necessary that this circuit shall not be normally closed in any of its springjacks 13, and accordingly it will be seen that though thejack shown has all the elements of the otherjacks of the system, the spring contacts 3 and 4 of the main telephone circuit are the only ones which are attached to circuit conductors; the others serving merely as plug guides whereby it becomes possible to employ the same plug connector P in association with this jack to give an order, as will thereafter be used to connect with the trunk jack 7c. By means of these order circuits the operations at the connecting board are readily kept under the control ofthe operator at the terminal board, and they are constantly employed for the transmission of orders relating to the connection of given trunk terminal plugs with desired lines.

There being two springjacks for each main circuit located at two different switchboards, it is essential that some'efcient means be provided whereby it may promptly and certainly be known at either springjack when a connection or a disconnection has been made at the other, or in other words, whereby the engaged or disengaged condition of a circuit at either switchboard may be determined at the other by a glance. And though not essential, it is desirable also that means should be provided at each connection board jack for promptly apprising the operator there, that a trunk conductor which has been in use, and which is plugged to said jack, is now disconnected, and that such plug therefore should now be Withdrawn. These requirements are met by the system of visual signals shown, in which a suitable visual indicator is closely associated with each connectingboard springjack j, and is operated first, by placing a connecting lplug in the corresponding or complementary jack Jof the same telephone circuit at the terminal board; and second by placing the terminal plug of any trunk conductorinthe connecting board jack j. A form of visual indicator which I have found well adapted for this purpose, is the self-restoring annunciator for which Letters Patent of the United States No. 481,120 were granted to Frank A. Pickernell, August 16, 1892; or, if desired an ordinary incandescent lamp may be employed, as indicated at the trunk signal of sect-ion a in Fig. l, and at section c5 in Fig. la. The former device I have illustrated in Fig. 6 of this specification, and it consists simply of a short electro-magnet a; which can be included in an electric circuit, and whose core has a curved tapering projection x2, extending through a hole in the shutter armature ac3. When current is passed th rough the coil, the shutter is drawn up, and when the current ceases, it is permitted to fall; in the first case announcing a connection,.and in the latter a disconnection. Such an indicator V placed beside its jack' at the connecting board has one ot' its coil terminals lOO IZO

nect with conducting surface 36 of plug P3, and thereby to be brought into circuit with battery F2. Itis united to the return conductor of said battery by the wire 50 through a revolving or vibratory circuit breaker R which may be kept in motion by suitable mechanism (not shown) or which in a manner well understood may be organized to start its motion as soon as current passes through it.

To indicate the busy condition of the line wanted, the plug P2 is inserted in the jack K and its battery conductor including the indicator o at the other end, is thus brought into circuit with the intermittent circuit breaker R, the current is intermitted through the said indicator which is thereby caused to flutter in response to the action of said circuit breaker, and the terminal board operator is thus visually informed that the line wanted is occupied. It is sometimes desirable that the calling substation should also receive a similar automatic notification, and I accomplish this by uniting' the main spring contacts 3 and 4 of the jack K which register with the main circuit conducting surfaces 33 and 34 of the plug, to a loop circuit extending through conductors 52 and 53 in which is included any convenient form'of battery signal transmitter, and a battery lf3. This signal may be of the same class as the circuit breaker B, or it maybe an ordinary buzzer; in an organization which has been constructed, I have however employed in this loop, a telephone transmitter t4, and have mounted the same in close j uXta-position to a phonograph p, which may be iu-constant operation, and arranged to repeat continuously into such transmitter the word busy, busy Any such signal is however transmitted over the several circuit conductors, from the trunk plug to the substation and is received in the telephone or upon the bell there, and the signal being heard, therein, automatically notifies the attendant that the line of the station called for is engaged with another connection. These devices however considered by themselves constitute the subject matter of another application for-Letters Patent iiled of even date herewith by myself, conjointly with Frank A. Pickernellfor an improvement in busy signals for telephone circuits, Serial No. 448,767, and, except as elements of a combination are therefore not claimed herein.

The operation may generally be described as follows: Station S signals the central station in the usual manner. lts circuitL as a1- ready stated is through aspring jack j located on the connecting board, extending thence to the corresponding or complementary springjack J at the terminal board A, section 01 and then to the terminal drop Z. The operator at the terminal board inserts the answering plug P of any connector c into the jack J and receives the call. This plug is for the present the terminal of the telephone loop, the threev way cam being properly turned; and the instructions of the substation are therefore properly received and answered. But the insertion of the plug in the jackJis an occupation of the circuit, and to forestall an interruption, by an attempt to connect'with the said circuit at its connecting board jack while such occupation continues, the operators at the said connecting board are to be informed that the circuit of station S is busy andthe springjackj therefore blocked. Thisis done by providing` that the insertion of the plug at J shall close a local circuit in which is located the signal receiver V located in close proximity to the jack The setting of this signal operates to prevent the connection of circuit L at the jack j of connecting board B, with the circuit of any other customer calling for station S, which connection otherwise might take place and interfere with the service. A similar electric visual indicator V2 protecting the springjack J at the terminal board A is not required to become operative, as the presence of the plug in the jack there, shows at once the line to be busy; and it does not become operative because no plug has been placed in springjack j to close its circuit. The operator at the terminal section a,having received the call from station S, finds that a connection with some other station,sayS2, is desired. It the circuits of station S and S2 should happen to be represented on the same or adjacent terminal boards, they may be at once connected directly with the regularlink connection or pair of switchboard cords Y in the ordinary way, and in that case the circuit L2 being connected through the connecting board to the terminal board, in the saine manner as is circuit L, the insertion of the plug in its terminal board jack would operate the visual signal V at its connecting board jack and would protect the connection from interference there, also in the same manner as in the case of circuit L. But the circuit L2 of station S2 as indicated in the drawing, is terminated at aremote terminal section a4,and must be reached through the connecting board. The operater therefore inserts the second plug P2 of the pair in the springjack 13 of the ordering or instruction circuit l2, extending from said springjack by branch 14 and main l2 to the head telephone of a switching operator stationed at some point b at the connecting board near to the line wanted. Over this, the said connecting board operator is instructed to connect line L2 of station S2with the office trunk conductor O, extending between the terminal board section ct to the pointb at the connecting board. The second plugfof the link connection Y would now be inserted in the jack k of the specified trunk as shown, and at the connecting board the plug terminal of said trunk would be inserted in the jack J2 of line L2of station S2. This last plug connection automatically operates the Visual indicator u at the terminal board end of the office truuk, and also severs the end of line L2 which extends to the terminal board a4 and actuates the visual indicator V2 of said line asso- IOO IIO

inbefore described, of an outer or connecting switchboard fitted with springjack connections, one for each line; an inner or terminal switchboard tted also with springjack connections, one for each line; a series of substation circuits passing through the connecting board and terminal board springjacks successively; ya plug connector forming the terminal of an operators telephone circuit, located at the terminal board, and adapted to t in the springjacks thereof for the purpose of answering calls; a visual signal associated with each springjack on the connecting board to indicate whether the circuit ot' such jack is busy; and a circuit changer associated with the corresponding springj ack on, the terminal board, controlling the said visual signal, the said circuit changer being arranged to be operated by the act of making a connection or disconnection, by inserting the said plug connector into the said corresponding springjack, for the purposes specied.

4t. The combination in a telephone central station apparatus, of an inner or terminal switchboard divided into operators sections; an cuter or connecting switchboard containing springjack connections; a series of telephone substation circuits entering the central station each passing th rough a single connecting board jack to a jack on that one ot the terminal boards at which is located its call annunciator; a series of office trunk conductors, extended from each terminal board to the connecting board, the terminal board end of each being provided with a spring jack, and the connecting board end with a lexibleconductor and plug, whereby the said trunks are adapted to serve as extensions through which a calling circuit at its terminal board may connect at the connection board with called circuits terminating at other sections; a series of double plug and cord connectors at each terminal section for uniting the main circuit jacks to the office trunk jacks; and an order or instruction circuit extended from theseveral terminal board sections to an operators telephone at the connecting switchboard, substantially as and for the purposes specified.

5. The combination in a telephone central station, of an inner or terminal switchboard, divided into operators sections containing a given number of springjacks or plug sockets, each section being provided with independent operating and supervisory apparatus; an outer or connecting switchboard having a springjack or plug socket for each entering circuit; a series of telephone circuits extended from substations, each passing first through one of thev connecting board jacks, and from thence inwardly to a jack at some one of the termi` nal boards; an office trunk conductorextended from each terminal board section to the connecting board, and adapted to serve as an extension circuit through which a circuit terminating in such terminal board section may connect with circuits terminating in other sections, at their respective connecting-board jacks; a series of link connectors at each terminal board section, each comprising a pair of jack plugs and flexible conductors uniting them; and an order or instruction circuit extended from each terminal board section to an` operators telephone at the connecting board, substantially as described.

6. In a telephone exchange, the combination, substantially as hereinbefore described, of a connecting switchboard; a sectional terminal switchboard; and a series of incoming substation lines, each connecting with a springjack at the terminal switchboard after passing through a similar spring jack or plugreceiving connection on the connecting switch board; with a series of plug and cord connectors containing double main circuit conductors at each terminal switchboard section for the purpose of connecting any two circuits together through their respective jack connections; three independent appliance circuit loops at each terminal board section, including respectively the operators telephones, the call sending generator, and the disconnecting signal device; and a three way cam switch for each of the said plug and cord connectors,in a bridge circuit between the said two main conductors thereof, controlling the connectionv therewith of the said appliance loops, for the purposes specilied.

7 In a telephone central office system, a divided switch apparatus comprising a terminal switchboard formed in sections, at which calls are answered and transmitted, and connections initiated, each section being provided with springjacks and annunoiators for a given number of main circuits; and ahomogeneous switchboard at which connections are made with circuits called for, the said switchboard being fitted with springjacks only, one for each entering main circuit, each located on its circuit at a point outside of the terminal board jackof the same circuit; in combination with a series of ofce trunk conductors extending from springjacks at each terminal section, to iiexible conductors and plugs located at one or more points of the said homogeneous switchboard; a series of double plug and flexible cord link connectors at each terminal section for making connections between the niain circuit and office trunk jacks; telephones and call receiving and sendingappliauces adapted by suitable switches (one for each cord) to be connected in derived circuit with the said link connectors; and iustruction or order circuits, extending between a springjack at each answering or terminal section, to whichthe operator may plug in and connect his telephones to an operators telephone at the connecting switchboard, substantially as described.

8. In a telephone central station switching apparatus the combination with a terminal switchboard at which calls are answered; a connecting switchboard at which the connection with a desired line may be made; a series of substation lines, each passing through IIO are located the terminal connection devices of main-line circuits, a series of trunk-lines extending between the two boards, having each a plug terminal at one end and a springjack at the other, a visual signal at the latter terminal, a circuit including said signal and including also a circuit controller, the latter being associated with the plug terminal, and being actuated whenever a connection is made thereby with any ot the terminal connection devices, substantially as described.

14. The combination with the two switchboards at which are located the terminal connection-devices or spring jacks of the maincircuits, of a trunk conductor extending be-v tween the two switch boards, a visual signal located at onefterminal of said trunk conductor, a circuit including said signal and also including a generator, said circuit being normally open at the other terminal of the trunk-conductor, and a circuit-closer at the latter terminal operated automatically by the act of making a connection thereat, so that the circuit of vsaid signal and its generator remains closed so long as said connection is eS- tablished, substantially as described.

l5. In a telephone central station apparatus a series of substation main circuits, each passing successively through two springjacks or like connection devices located on different switchboards; and a series of office trunk conductors extending from one ofthe said switchboards where each said trunk has a springjack terminal, to the other Where each has a plug terminal; combined with a Visual signal indicator located at each springjack of the said main circuits and tru nk conductors, cach adapted to respond to connections or disconnections made at the other jack of such main circuits, and at the plug end of such trunk conductors respectively, by means of circuit closing contacts electrically connecting with said indicators, and operated by the act of making such connections and disconnections.

16. In a telephone central oiiice system, a divided switching apparatus comprising a terminal or answering switchboard formed in sections to which a determinate number of substation circuits are assigned; a non-sectional connecting switchboard on which all substation main circuits are represented bya plug socket or jack; a series of such main circuits connected serially with the connecting board and with some one section of the terminal board; oiiice trunk conductors extending from the sections of terminal board,

Ato different points at the connecting board means for automatically operating the same at either jack ot any circuit by inserting a plug in or withdrawing it from the remaining jack of such circuit; and an auxiliary system of visual signals associated with each office trunk conductor, and comprising an electric indicator located at vthe end or ends thereof, and a circuit controller therefor at the opposite end thereof, arranged to be actuated by any electric connection or disconnection made at such opposite end, whereby such use or disuse of either end, may be indicated at the other; all substantially as hereinbefore described.

17. In a telephone central otiice switching apparatus, the combination with a series of main circuits, anda series of trunk conductors, each of both series being furnished with a pair of connection devices, whereby it may be connected with others; of a series of normally open signal circuits extending each between the two members of a pair of the said connection devices; a visual signal indicator in such circuits located at each connection device of each pair, and a circuit closer for each such circuit and indicator, located and associated with the remaining connection device of the said pair, and adapted to be actuated by each connection or disconnection made therewith; whereby such connections or disconnections of main circuits made by either member of a pair of connection devices are enabled simultaneously to make or break its associated signal circuit, and to automatically announce themselves at the other mem- Iber of said pair.

i 18. 'The combination of a telephone central office switchboard apparatus in which each substation circuit is provided with connection devices such as springjacks, one at each of two independent switchboards, said apparatus also including a series of oftice trunk conductors extending between the said two independent switchboards for the purpose of connecting a jack of a given circuit at one of the switchboardsgwith a jack of a second circuit at the other switchboard, each trunk conductor being fitted at both ends with suitable connection devices; and a system of automatic visual electric signals operated by means of local signaling circuits for the purpose of indicating at either connection device of the said substation circuits and trunk conductors the engagement or disengagement of the other connection device thereof, each signal consisting of an electric indicator associated with each of the said connection devices, and adapted to respond to connections and disconnections made at the other connection device of each such circuit or conductor; substantially as described.

19. The combination of a telephone switchboard apparatus in which each substation circuit is provided with two connection devices such as springjacks, one at each of two independent switchboards, said apparatus also including a series of oflice trunk conduct- IOO ing board terminal thereof, with a visual indicator adapted to respond with a distinctive signal to either current and to indicate alternatively thereby at the answering board, that connection is made with the circuit wanted, or that said circuit is busy.

25. In coinbinationwith an office trunk conductor extending between an answering or terminal switchboard, anda connection completingswitchboard co mprisingaseries of suitable springjacks, one for each main circuit; and a busy signal springjack located at such connecting switchboard; a system of visual signals for indicating at the said answering board the progress of a connection at the connecting board, said system consisting of a signal circuit extending in association with said trunk between said switchboards, and being normally open at the connection board; a source of electricity therefor; two alternative circuit closers therefor at the connecting board, one located upon each main circuit springjack adapted to complete the signal circuit directly, and to establish a steady current therein when the trunk conductor is connected with said main circuitjack; and the other located upon the busy signal jack and adapted to complete the said signalin g circuit through a vibrator; a buzzer or a current varying device, and thus to produce a varying current therein when the said trunk conductor is connected with said busy signal jack; and a visual signal indicator included in the said signal circuit at the answering board, and adapted to give distinctive signals in response to, and corresponding with the said circuit closer-s respectively, substantially as described.

26. In combination with a main telephone circuit extending from an outstation through an answering switchboard to an independent switchboard at which are located the connection devices of other main circuits, with which said circuit may be connected for through communication; and an audible signal receiving instrument such as a telephone includedl therein at such outstation; a local signaling circuit extendingin association with said main circuit from the said answering switchboard to the said independent switchboard; a visual indicator included therein at said answering switchboard; and a compound busy signal transmitter at said independent switchboard, providedwithindividual transmitting devices for the said main and local circuits respectively, and adapted to be connected with said circuits and thereby to simultaneously operate said audible and visual signal receivers, each over its own circuit;substantially as and for the purposes specified.

27. In atelephone exchange system,the combination of a series of main circuits, extending from substations to a central station where each passes successively through two springjacks; a homogeneous connecting switch,-`

board at which the first springjack of each main circuit is placed; a sectional terminal switchboardvon which the inner spring jack of all lines are placed; a series of oftice trunk conductors, eachextending from a springjack at some one ot'the terminal board sections to the connecting board, and being there provided with a flexible cord and plug terminal whereby connection may be made between a calling line at a terminal board-fand a called line at the connecting board; a series of link connections at each terminal board section, consisting each ot liexible conductors with a plug connector at both ends, whereby any main circuit jack may be connected with any other, or with any trunk conductor jack; a busy signal springjack at the connecting switchboard, provided-with the spring terminals of two independent arbitrary sign al electrotoines or other signal transmitting devices; and an automatic i signal circuit associated with each tru nk conductor and-comprising an electric generator, a visual indicator located at the terminal board,tan electric conductor extendin g from said indicator to a contact surface on the trunk conductor plug terminal at the connecting board; and return conductors connected respectively with an auxiliary springcontact in the line jacks at said board, and with the spring terminal of one of the busy jack signal transmitters, the said contacts being adapted to register with the plug contact surface of said signal circuit, and the terminals of the remaining busy jack signal transmitter being adapted to register. and connect with the contact surface of the trunk conductor proper, whereby the said plug when inserted in a main circuit jack at the connecting board, is enabled to connect the said circuit through the trunli'with any other main circuit united with the said trunk at the terminal board and to establish at said terminal board a steady signal indicating the occupancy of said trunk; and when insertedin the busy signal jack to send an arbitrarybusy signal over a main circuit connected at the terminal board with said trunk to the substation of such line, and establish a liutteringor other distinctive signal at said terminal board indicating that the line called for is busy, substantially as described.

28. A telephone central office system, comprising in a single organizat-ion, an outer or connecting switchboard; an inner or terminal sectional switchboard; a series of main circuits extending from telephone snbstations, all passing iirst through a springjack on the connecting board, and each continuing thence to a duplicate springjack on a given section of the terminal board; aseries of office trunk conductors, extending from each terminal section to different points on the connecting board, each being provided with aspringjack normally closed through an annunciator at the terminal board and ending in a connecting plug at the connecting board; a series of double plug connecting cords at each terminal board section,.for uniting the jacks of dilerent circuits or for uniting a circuit jack with IOO 

